I have been trying to improve my songwriting, and have hit a block when it comes to vocal harmonies. To train myself in this regard I have been listening to a lot of Beatles tunes and other rock songs that involve harmonies, and I am having a really hard time picking them out. I can usually sing along with the main vocals, but if I try to sing the harmony parts I get stuck pretty quickly.
I am sure voice lessons would be the best path to take, but that's not an option for me right now, but I hope to take some eventually. For the time being, I have done some research on constructing vocal harmonies and learned about using thirds and sixths, contrary motion, certain intervals to avoid etc., but I want to figure out how to begin to hear the different voices in a given song and eventually be able to pick out a part and sing along with it. I would assume more work on recognizing intervals would help, but is there anything more specific to vocal harmonies I can do to follow along?